1,1-Dichloro-1-fluoroethane is presently under consideration as a replacement for trichlorofluoromethane as a foam blowing agent. It has a substantially lower ozone depletion index than trichlorofluoromethane. Moreover, 1,1-dichloro-1-fluoroethane displays a 10-15% greater blowing efficiency in rigid foam, and improved solubility in aromatic polyester polyol, in comparison to trichlorofluoromethane. However, there is as yet no acceptable method for the efficient production of 1,1-dichloro-1-fluoroethane which is suitable for large scale commercial exploitation.
The liquid phase reaction of hydrogen fluoride and vinylidene chloride was reported by Henne and Plueddeman, J. Amer. Chem. Soc. 65, 1271 (1943). A mixture of hydrogen fluoride and vinylidene chloride was heated in a 4:1 molar ratio in an autoclave at 65.degree. for 3 hours to give 50% 1,1-dichloro-1-fluoroethane, traces of 1-chloro-1,1-difluoroethane 10% of unreactive vinylidene chloride, 5% of 1,1,1-trichloroethane and 15% tar.
Henne and Arnold, J. Am. Chem. Soc. 70:758 (1945) describe the BF.sub.3 -catalyzed addition of hydrogen fluoride to various chlorofluoroolefins in the liquid phase at a molar ratio of HF to olefin of 2:1 at 95.degree. C. However, the process is characterized by very low vinylidene chloride conversion, polymer formation, and lack of selectivity for the desired product.
More recently, several patents issued to Dynamit Nobel teach a gas phase, catalyzed reaction of vinylidene chloride and hydrogen fluoride. The only major product reported is 1,1,1-trifluoroethane in 98.8% to 99.8% yield, with very little or no 1,1-dichloro-1-fluoroethane produced. The reactions of vinylidene chloride and hydrogen fluoride disclosed by the aforesaid Dynamit Nobel patents are summarized in Table 1:
TABLE 1 __________________________________________________________________________ REACTION CONDITIONS RATIO PRODUCTS DISTRIBUTION (vol. %) PAT. NO. CATALYST TEMP. (.degree.C.) HF:Cl.sub.2 C.dbd.CH.sub.2 CCl.sub.2 FCH.sub.3 CClF.sub.2 CH.sub.3 CF.sub.3 CH.sub.3 Cl.sub.2 C.dbd.Cl __________________________________________________________________________ U.S. Pat. Bi(NO.sub.3).sub.3 over Al.sub.2 O.sub.3 180 3.2 0 0.2 99.7 0.1 No. 3,904,701 Bi(NO.sub.3).sub.3 over Al.sub.2 O.sub.3 205-220 3.7 0 0.2 99.8 0.1 Bi(No.sub.3).sub.3 over Al.sub.2 O.sub.3 210-225 3.3 0 0.4 98.9 0.7 Bi(No.sub.3).sub.3 over Al.sub.2 O.sub.3 215-225 3.4 0 0.2 99.6 0.2 U.S. Pat. CrCl.sub.3 /Al.sub.2 O.sub.3 150 3.5 (molar) 0.2 0.2 99.8 0.8 No. 3,803,241 British Pat. Mn(NO.sub.3).sub.2, Bi(NO.sub.3).sub.3 180 3.3 (volume) 0 0.3 99.6 0.1 No. 1,309,361 over Al.sub.2 O.sub.3 180 3.3 (volume) 0 0.2 99.7 0.1 __________________________________________________________________________
In 1947, McBee et al. reported the liquid phase reaction of hydrogen fluoride and vinylidene chloride in a molar ratio of from 6.6:1 to 5.4:1, in an autoclave at between 140.degree. C. and 210.degree. C. under 5,000-6,000 psi pressure, using diphenylamine as a polymerization inhibitor. McBee et al., Ind. Eng. Chem. 39, 409-12 (1947). The authors reported in Table II yields of fluorinated product up to 90%. At a temperature of 140.degree. C. the yield of fluorinated product was 76%. No 1,1-dichloro-1-fluoroethane was isolated. U.S. Pat. No. 2,637,747 discloses a similar process.
More recently, a liquid phase process for making 1-chloro-1,1-difluoroethane was disclosed in British Patent 1,556,131. A mixture of vinylidene chloride and hydrogen fluoride was heated in the presence of catalytic amounts of SnCl.sub.4 in an autoclave at 60.degree. C. to form 1,1-dichloro-1-fluoroethane (64.8%), 1-chloro-1,1-difluoroethane (26.7%), 1,1,1-trifluoroethane (2.1%), 1,1,1-trichloroethane (0.8%), oligomer (1.4%), and 4.2% unreacted vinylidene chloride. However, liquid phase reactions, which are generally conducted in batch rather than continuous fashion, are less desirable for economic reasons. Gas phase reactions are generally favored, as they are more readily adapted for continuous operation, and hence achieve maximum utilization of catalysts.
The various prior art processes involving hydrofluorination of vinylidene chloride have relatively low selectivity for 1,1-dichloro-1-fluoroethane. Clearly what is needed is a process capable of efficient gas phase conversion of vinylidene chloride with high selectivity for 1,1-dichloro-1-fluoroethane.